$$s^3+36s^2+564s+3311 = 0$$
Answer
$$ \begin{matrix}s_1 = -11.99242 & s_2 = -12.00379+11.48913i & s_3 = -12.00379-11.48913i \end{matrix} $$
Explanation
This polynomial has no rational roots that can be found using Rational Root Test.
Roots were found using qubic formulas.
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Polynomial Equations Solver